Benzoic acid (carboxybenzene) is used to make a large number of chemicals. For example, benzoic acid is used to produce benzoyl chloride, by treatment of benzoic acid with thionyl chloride, phosgene or one of the chlorides of phosphorus. Benzoyl chloride is an important starting material for several benzoic acid derivates like benzyl benzoate, which is used for artificial flavors and insect repellents. Benzoyl peroxide is obtained by treatment of benzoic acid with peroxide. The peroxide is useful as a radical starter in polymerization reactions and also a component in cosmetic products. Benzoate plasticizers, such as the glycol-, diethylengylcol-, and triethyleneglycol esters are obtained by transesterification of methyl benzoate with the corresponding diol. Alternatively these species arise by treatment of benzoylchloride with the diol. These plasticizers are used similarly to those derived from terephthalic acid ester. Phenol is obtained by oxidative decarboxylation of benzoic acid at 300° C. to 400° C. Benzoic acid is also used as a food preservative, and as a constituent of ointments for the treatment of fungal skin diseases and acne.
The methylbenzoic acids are used in various industrial processes, including the production of chemicals, drugs, paints, and enamels. 4-Methylbenzoic acid (p-toluic acid) is a substituted benzoic acid that is used in the chemical industry to make terephthalic acid, which, in turn, is used industrially to produce polyethylene terephthalate (PET). PET is a thermoplastic polymer resin of the polyester family and is an important raw material used in synthetic fibers. It is also used in the manufacture of a wide variety of containers, in thermoforming applications, and in resins combined with glass fiber. 3-methylbenzoic acid (m-toluic acid) is used industrially as a precursor in the production of the insecticide DEET (N,N diethyl-m-toluamide), among other uses. 2-methylbenzoic acid (o-toluic acid) is widely used as a raw material for agricultural chemicals, medicines and polymerization initiators.
Benzoic acid and the 2-, 3-, and 4-methylbenzoic acid isomers are typically produced by partially oxidizing toluene or o-, m-, and p-xylene, respectively, with oxygen or air. On an industrial scale, both of the methyl groups in p-xylene are oxidized by oxygen or air to produce terephthalic acid (benzene-1,4-dicarboxylic acid or p-phthalic acid). Such processes are strongly influenced by a number of factors, such as temperatures, pressures, and the nature of the catalyst used, if any. Appropriate selection of these factors is important, as selection influences the reaction trend, the reaction velocity, and the overall technical and economic balance of the production, both in terms of yield and catalyst consumption, and also from the point of view of the intricacy and costs of installation and upkeep. These costs are influenced, for example, by the pressures attained, the consumption of thermal energy for reaching desired temperatures, and the intricacy and the number of component parts of the installation. For instance, in many applications it is desirable to enhance the degree of conversion of toluene or xylene. While increasing the reaction pressure may increase reaction rate, it also increases wear of the materials constituting the reactors, the pipings, and the mechanical parts of the plant, as well as any ancillary devices. Most existing processes and production facilities for making benzoic, methylbenzoic acids, and phthalic acids are subject to a variety of constraints such as product yield, plant size, energy consumption and mass flow limitations. Accordingly, there is continuing interest in improving the ways that benzoic acid, methylbenzoic acid isomers, and phthalic acid isomers are produced.